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1. Define the concept of assertions. 1 Explain the use of assertions. 2 Create Java program using assertions. 3 Run Java program using assertions. 4 2.

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Presentation on theme: "1. Define the concept of assertions. 1 Explain the use of assertions. 2 Create Java program using assertions. 3 Run Java program using assertions. 4 2."— Presentation transcript:

1 1

2 Define the concept of assertions. 1 Explain the use of assertions. 2 Create Java program using assertions. 3 Run Java program using assertions. 4 2

3 3 Assertion are a way to test certain assumptions about the logic of a program. It is used to generally to test assumptions about local program logic inside a method and usually not to test that external expectations are met. One important feature of assertions is that they can be removed entirely from the code when it runs. This makes it possible for you to enable assertions during program development, but to not have the tests executed at runtime when the final product is delivered to a customer. This is n important difference between assertions and exceptions.

4 Syntax of an assertion is: assert ; assert : ; If evaluates false, then an AssertionError is thrown. The second argument is converted to a string and used as descriptive text in the AssertionError message. 4

5 5 Assertions use to document and verify the assumptions and internal logic of a single method: Internal invariants Control flow invariants Postconditions and class invariants Inappropriate uses of Assertions Do not use assertions to check the parameters of a public method. Do not use methods in the assertion check that can cause side-effects.

6 6 The problem is: 1 if (x > 0) { 2 System.out.println(x more than 0); 3 } else { 4 System.out.println(x equals or less than 0); 5 } The solution is: 1 if (x > 0) { 2 System.out.println(x more than 0); 3 } else { 4 assert ( x == 0 ); 5 System.out.println(x equals to 0); // unless x is negative 6 }

7 7 For example: 1 switch (suit) { 2 case Suit.CLUBS: //... 3 break; 4 case Suit.DIAMONDS: //... 5 break; 6 case Suit.HEARTS: //... 7 break; 8 case Suit.SPADES: //... 9 break; 10 default: assert false : "Unknown playing card suit"; 11 break; 12 }

8 8 For example: 1 public Object pop() { 2 int size = this.getElementCount(); 3 if (size == 0) { 4 throw new RuntimeException("Attempt to pop from empty stack"); 5 } 6 7 Object result = /* code to retrieve the popped element */ ; 8 9 // test the postcondition 10 assert (this.getElementCount() == size - 1); return result; 13 }

9 If assertion checking is disabled, the code runs as fast as if the check was never there. Assertion checks are disabled by default. Enable assertions with the following commands: >java -enableassertions MyProgram or: >java -ea MyProgram Assertion checking can be controlled on class, package and package hierarchy bases, see docs/guide/language/assert.html


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